This invention relates to a method of filling with a volatile liquid at least one tank of a multi-tank installation. The invention further relates to a multi-tank installation for storing volatile liquids, and also to a valve for use in such a multi-tank installation.
Though this invention may be used with a variety of volatile liquids, it find particular application in the filling of underground storage tanks for petrol, as commonly provided at a petrol filling station for motor vehicles. Consequently the invention will be hereinafter be described expressly with reference to that application, though it is to be understood that the invention is not limited to that application.
The usual arrangement at a petrol filling station having a plurality of underground storage tanks is for each tank to have a respective fill pipe through which the tank may be filled with petrol off-loaded from a road tanker. Each tank has a respective first vent pipe, the first vent pipes of all of the tanks being connected together and to a common air egress and inlet pipe provided with a so-called pressure-and-vacuum valve to permit the ingress of air when the pressure within the tanks falls below some pre-set value, as well as releasing excess pressure. This permits the pumping of fuel out of any of the tanks, when demanded by a petrol pump for delivery to a vehicle, as well as safety during the off-loading of petrol from a tanker.
All of the tanks also have a further common vent pipe which is normally closed off but which is connected to a vapour recovery system provided on the road tanker when a delivery of petrol is being made to a tank. The vapour recovery system applies a low level of suction to the further vent pipe as a delivery is being made, to draw air laden with petrol vapour from the tank being filled and to return that vapour to a tank of the road tanker.
It will be appreciated that with the above described arrangement, petrol vapour driven from a tank being filled is returned to the road tanker. Though the volume of petrol vapour recovered in this way on filling any one tank may not be very high, and typically equivalent to only a liter or so of liquid petrol, over a period of time when a considerable number of tanks have been filled, there is a significant marginal loss to a site operator.